Re: Impressions dropped after changing from CPC to CPA.

It's typical for impressions to drop slightly as Google is more selective about where your ad is shown but a drop that substantial likely means trouble. It likely means that your CPA bid isn't high enough. Did you set your CPA bid lower than the CPA you were previously getting with CPC bidding?

Re: Impressions dropped after changing from CPC to CPA.

The CPA bid is the recommended bid from Adwords and matched the historical number. Did not change it. However, the CPC is lower than it used to be in the change. But there is no way to affect the CPC now that the system is on CPA.

Re: Impressions dropped after changing from CPC to CPA.

Hi Raz, how many conversions did you see in the past 30-day period? How many Keywords/Groups were these conversions spread across?

It's really important that CPA strategy Campaigns have enough data to make reasonable decisions. You may have a Campaign with 50 conversions in a month, but if you've got 200 Keywords, and those 50 conversions came from just 10 of them, the other 190 - to the conversion optimiser - are effectively non-performers and may have dramatically reduced CPCs and therefore impressions.

CPA targeting works best where every Keyword in the element (Campaign/Group) has a statistically significant conversion history. Without this history, the AdWords optimiser can only assume the Keyword isn't performing.

Re: Impressions dropped after changing from CPC to CPA.

It is normal for a campaign that has been shifted from CPC to CPA to see a drop in impressions. Using historical conversion data in the campaign, CPA bidding basically tries to show your ads at instances or in your case placements ( since its a ICM targeted campaign) where you are more likely to record conversions. This is because, CPA bidding is part of Conversion Optimizer.

As you mentioned your CTR have remained constant and your CPC have gone down, this is a factor of the CPA bidding model trying to record conversions according to the desired CPA you have set (Target CPA) or the under the maximum limit that you have set for CPA i.e. Max CPA. Just remember, post the switch, your campaign is bound to behave erratic for sometime and then eventually settle down and start performing for you as soon as it finds its very own sweet spot.